An extruder-calender combination of this kind has become known through DE-OS 38 06 387. In this apparatus, a thick sheet of uniform thickness is extruded from the mouthpiece of the wide extrusion head and, before it passes it through the narrowest place of the roller gap, is drawn through a not essentially larger gap with the help of one of the two calender rollers and pressed by the extrusion pressure. In this gap space between the fixed forming tool with a concave cylindrical surface and the rotating calender roller, the macro molecules of the material are alinged in a forward direction. It is thereby achieved that the extruded and in this manner aligned material is not further thinned after leaving the narrowest part of the roller gap. The products produced by this equipment have outstanding homogeneity and the property of not being reduced in width past the narrowest part of the roller gap. However, changing to other materials can make it necessary to change the active faces of the fixed forming tool with a concave cylindrical surface facing a calender roll. Also it is not possible, with this apparatus, to change the working of the material in the gap between a calender roller and the stationary forming tool.
Through U.S. Pat No. 32 74 645 it is known to make the mass distributor of an extruder-calender combination inter-changeable. Here the inter-changeable distributor is made in two parts and envelpoes a part of the upper calender roller. A working of the extrudant through the one calender roller and the opposed stationary forming tool does not here occur. As with the above mentioned apparatus, it is also necessary here to disassemble the entire extrusion head in order to change the screw.
Through DE-OS 20 04 888 there is known an interchangeable distributor which provides a variable resistance for the production of thinner or thicker sheets. With the present day requirements of versatility with respect to mixtures that are difficult to work, this construction is no longer sufficient. With this extrusion head, changing the screw is possible only after full disassembly of the extrusion head.
The mass pressure applied by the extruder depends decisively on the head resistance, thereby also the energy conversion of the screw and hence the plasticification and warning of the mixture in the extruder. The latter limits the rate of rotation of the extruder screw and thereby limits the rate of production. There has hence been an effort to carry out a small , but definite part of the homogenization and decomposition work through the rollers of the calender, thereby making it possible to drive the extruder with limited energy consumption.
DE-OS 24 50 225 uses conventional nozzel lips which are of variable length in the direction of flow in order to influence, in large steps, the kneading work effected by the rollers of the calender. It is thereby overlooked that, for example, shorter lips result in a pressure decrease in the head and thereby an essential decrease in energy exhange in the extruder, wherefore an essentially greater energy exchange in the kneading must be effected. This can result in partial overheating or squeezing action or the inclusion of air which is objectionable. Hence this principle is in practice very unfavorable because a nozzle lip change is very time and labor consuming. This system does not provide an optimal operation. Also with this extrusion head, a disassembly of the head is required when it is necessary to change the screw.